A significant volume of pollutant materials, e.g., carbon monoxide, unburned hydrocarbons and the like, are generated at the time of start-up by internal combustion engines, whether stationary or mobile, and whether spark or compression ignited. The reason for this is that it takes a finite amount of time, e.g. 15 to 60 seconds, for the catalyst in the catalytic converter, now generally associated with such engines, to reach optimum conversion temperature from the heat of the exhaust alone. The catalyst is not optimally effective. To overcome this problem, there have been developed several types of electrically heatable catalytic converters which shorten the time within which the catalytic converter reaches optimum operating temperature. Typical of the efforts in this direction are those of Kitzner as evidenced by his U.S. Pat. Nos. 3,768,982 and 3,770,389 each dated Oct. 30, 1973. More recently, electrically heatable catalytic converter cores have been formed using the resistance of corrugated thin metal strips connected across a voltage source as a means of heating the core to a desired temperature (e.g., at least about 600 degrees F.). Reference may be had to the copending application of Cornelison and Whittenberger Serial No. 196,301, filed May 20, 1988.
The present invention is an improvement on the structures of the prior art and is based on the discovery that a refractory metal oxide, applied as a wash coat to a thin stainless steel strip and fired to fix the coating, (such as taught in the U.S. Pat. to Cornelison et al 4,711,009 dated Dec. 8, 1987) will not adhere to a masking agent, e.g., a brazing alloy, particularly a nickel brazing alloy or a silver brazing alloy. The refractory metal oxide, e.g. alumina, does not conduct electricity although it is a substrate of choice for a catalyst, such as a noble metal catalyst. The brazing alloy is conductive. Hence, one is now able to prepare a catalytic core element from a thin stainless steel strip with electrically conductive areas adjacent to catalyst containing areas, place a plurality of such core elements in stacked relation, and apply a potential through the electrically conductive areas and utilize the resistance of the thin metal laminae to effect heating of the entire core. The disclosure of the aforesaid Patent 4,711,009 is incorporated herein by reference thereto to obviate the necessity for reproducing large portions thereof herein.